Background & Aims: Recently, the role of English has shifted from the more general perspective of every day usage to a narrower situation and task specific perspective. Many experts in the field argue that Learners need English for a particular task or a field of study and successful courses are those that concentrate on one particular area in teaching English. Accordingly, the present study attempts to investigate the issue of whether the English teacher or the field specialist or their cooperative instruction is more effective.

Materials & Methods: Three groups of 130 medical students participated in this study. The first experimental group taught by cooperation of both an English teacher and a field specialist and also, two other experimental groups, one taught by a field specialist alone and the other taught by an English teacher. One test of reading comprehension was developed, which was used both for the pretest and the posttest; besides, a vocabulary test was designed, which was used both for pre and posttests. Mixed methods experimental research design was utilized for the present study.

Results: Both qualitative and quantitative analyses revealed that the class taught by the cooperative method held more positive attitudes toward learning English and they paid more attention to reading skill.

Conclusion: The findings of the study showed that among language skills, reading was considered the most important by the students, and cooperative teaching was so effective in students' achievements in both reading comprehension and vocabulary tests.

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